Monitoring AlmaLinux 9 with SNMP in Nagios XI: A Step-by-Step Guide

Effective Linux server monitoring is essential for ensuring performance and reducing downtime. Simple Network Management Protocol (SNMP) provides an agentless solution to monitor AlmaLinux 9 servers using Nagios XI.

This guide walks you through the process of installing and configuring SNMP on AlmaLinux 9 and integrating it with Nagios XI for centralized, real-time system visibility.

Prerequisites

Before proceeding, make sure you have:

• AlmaLinux 9 with root or sudo privileges
• A running Nagios XI server with the SNMP wizard enabled
• Network connectivity between AlmaLinux and Nagios XI

Step 1: Install SNMP on AlmaLinux 9

1. Install the SNMP daemon and utilities:

sudo dnf install net-snmp net-snmp-utils -y

sudo dnf install net-snmp net-snmp-utils -y

2. Verify SNMP installation:

snmpd -v

snmpd -v

Step 2: Configure SNMP Access

SNMP v2c Configuration

1. Backup the default config:

sudo cp /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.bak

sudo cp /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.bak

2. Edit the configuration file:

sudo nano /etc/snmp/snmpd.conf

sudo nano /etc/snmp/snmpd.conf

3. Add the following line (replace with your Nagios XI server IP):

rocommunity Str0ngC0mmunity 10.25.5.12

rocommunity Str0ngC0mmunity 10.25.5.12

4. Restart SNMP:

sudo systemctl restart snmpd.service

sudo systemctl restart snmpd.service

SNMP v3 Configuration (More Secure)

1. Stop SNMP temporarily:

sudo systemctl stop snmpd.service

sudo systemctl stop snmpd.service

2. Create a secure SNMP v3 user:

sudo net-snmp-create-v3-user -ro -a SHA -A Str0ng@uth3ntic@ti0n -x AES -X Str0ngPriv@cy nagios

sudo net-snmp-create-v3-user -ro -a SHA -A Str0ng@uth3ntic@ti0n -x AES -X Str0ngPriv@cy nagios

3. Restart SNMP:

sudo systemctl restart snmpd.service

sudo systemctl restart snmpd.service

Step 3: Configure Firewall Rules

If firewalld is active:

sudo firewall-cmd --zone=public --add-port=161/udp --permanent
sudo firewall-cmd --reload

sudo firewall-cmd --zone=public --add-port=161/udp --permanent
sudo firewall-cmd --reload

Confirm the rule:

sudo firewall-cmd --list-ports

sudo firewall-cmd --list-ports

Step 4: Enable SNMP on Boot

sudo systemctl enable snmpd.service

sudo systemctl enable snmpd.service

Step 5: Test SNMP Communication

Run from Nagios XI server:

For SNMP v2c:

snmpwalk -v2c -c Str0ngC0mmunity 10.25.5.12

snmpwalk -v2c -c Str0ngC0mmunity 10.25.5.12

For SNMP v3:

snmpwalk -v3 -u nagios -l authPriv -a SHA -A Str0ng@uth3ntic@ti0n -x AES -X Str0ngPriv@cy 10.25.5.12

snmpwalk -v3 -u nagios -l authPriv -a SHA -A Str0ng@uth3ntic@ti0n -x AES -X Str0ngPriv@cy 10.25.5.12

Expected output:

iso.3.6.1.2.1.1.1.0 = STRING: "Linux almalinux 9 ..."

iso.3.6.1.2.1.1.1.0 = STRING: "Linux almalinux 9 ..."

If no output appears, verify SNMP configuration and firewall.

Step 6: Add AlmaLinux Host to Nagios XI Using SNMP Wizard

1. Log into Nagios XI.

2. Go to Configure > Run a configuring wizard.

3. Select Linux SNMP wizard.

4. Enter AlmaLinux 9 IP and SNMP settings (community string or SNMP v3 credentials).

5. Choose metrics (CPU, memory, disk, processes).

6. Apply configuration and verify monitoring.

Common Issues & Fixes

SNMP Not Running

sudo journalctl -u snmpd --no-pager | tail -20
sudo systemctl restart snmpd.service

sudo journalctl -u snmpd --no-pager | tail -20
sudo systemctl restart snmpd.service

Host Appears “Down” in Nagios XI

sudo firewall-cmd --list-ports
sudo systemctl status snmpd

sudo firewall-cmd --list-ports
sudo systemctl status snmpd

SNMP Credential Errors

• Confirm SNMP version and credentials in both AlmaLinux and Nagios XI
• Restart SNMP after any changes

Conclusion

You’ve successfully configured AlmaLinux 9 for SNMP monitoring in Nagios XI. This setup allows for secure, agentless tracking of system metrics in real-time. For advanced use, explore custom SNMP OIDs or additional Nagios XI plugins.

If you’d like to learn how to monitor Linux machines with Nagios XI 2024 and 2026 using SNMP, check out this doc.

For support:

• Nagios Support Forum
• Nagios Knowledgebase